Cholesteatoma of the middle ear is an epidermal cyst formed from keratinizing stratified squamous epithelium. Most commonly caused by a retraction of the tympanic membrane from inflammation due to chronic infection, perforation of the tympanic membrane, or incomplete clearance of squamous debris from the external auditory canal. Rarely, it is congenital. Early on, the patient may complain of mild hearing loss, which can progress to a plugged-ear feeling. The patient will likely experience continuous drainage / otorrhea and possibly dizziness. More advanced disease can invade the skull base, injure the facial nerve, and cause significant conductive and sensorineural hearing loss.